Closed cryogenic cooling system without moving parts

ABSTRACT

The system generally includes an electrochemical pump for pressurizing a cryogenic gas, a heat exchanger for cooling the gas to below its inversion temperature, a Joule-Thomson flow restrictor to cool the gas by adiabatic expansion, a load heat exchanger that is thermally coupled to an electronic component or surface that requires cryogenic cooling, and a low-pressure flow path back to the pump. One or more reservoirs can be provided in the high-pressure and low-pressure flow paths. The flow paths can be thermally coupled by one or more regenerative heat exchangers. The electrochemical pump can be adapted to transport either protons or hydronium ions. Protons are preferably transported using pump components that do not contain water in any chemical form. Either hydrogen or oxygen can serve as the cryogen. Where hydrogen is the cryogen, the high-pressure flow path can be provided with a catalytic surface to convert ortho-hydrogen to para-hydrogen, and the low-pressure flow path can bear a catalyst to promote the reverse reaction.

FIELD OF THE INVENTION

This invention relates to closed systems for providing cryogenic coolingto electronic components such as space-based surveillance sensors.

BACKGROUND OF THE INVENTION

Various electronic devices and systems are designed to operate atcryogenic temperatures, well below liquid nitrogen temperatures.Infrared sensors, demagnetization devices, infrared interferometers,cryogenic optics and filters, and low noise cryogenic electronic devicesare representative electronic components that require cooling atcryogenic temperatures. For applications of short duration, cryogenicdewars are useful for providing cryogenic cooling to such electroniccomponents and other devices. However, a closed loop refrigerationsystem is required for applications that must be conductedintermittently or continuously over a long period of time, such ascertain spacecraft experiments, interplanetary missions, and processingand manufacturing in space.

Closed cryogenic cooling systems typically employ a Joule-Thomson flowrestrictor to reduce the temperature of a cryogen such as hydrogen,helium, nitrogen, oxygen, air, or methane. The cryogenic gas istypically compressed and then cooled to well below its inversiontemperature in a regenerative heat exchanger prior to beingadiabatically expanded through the Joule-Thomson flow restrictor. Theexpansion can be made to liquify part of the gas. The expanded gas isrecirculated in a closed loop through a compressor of conventionaldesign. See U.S. Pat. No. 3,415,077; U.K. Pat. No. 1,433,727; Lerner,E., et al., Cryogenics, pp. 548-550, September 1975. Mechanicalcompressors are considered unreliable for long-term and intermittentapplications, making them unsuitable for spacecraft applications. Acryogenic refrigeration system with no moving parts would enhance theoperating lifetime and reliability of cryogenically cooled electroniccomponents sent into deep space and other environments where maintenanceis impossible or impractical. Recently, molecular absorption compressorshave been incorporated into closed cryogenic cooling systems containingonly a few moving parts, but the metal halide pumps must be staged toachieve the compression and in addition require sophisticated feedbackcontrol. See AIAA Papers Nos. 82-0830 and 84-0058.

Electrochemical pumps, described for example in U.S. Pat. Nos. 3,489,670and 4,118,299, typically compress hydrogen by transporting hydrogen ionsacross a solid polymer membrane containing water in some form.

SUMMARY OF THE INVENTION

A closed cryogenic cooling system with no moving parts includes anelectrochemical pump for pressurizing an ionizable cryogenic gas such ashydrogen or oxygen. The electrochemical pump delivers a pressurized gasstream into a high-pressure flow path. Provision is made to remove anyentrained water vapor. One or more heat exchangers are provided in thehigher-pressure flow path for cooling the pure gas to below itsinversion temperature prior to delivery through a Joule-Thomson flowrestrictor into a load heat exchanger that is thermally coupled to anelectronic component or surface that requires cryogenic cooling. Alow-pressure flow path shuttles the expanded gas from the load heatexchanger to the electrochemical pump. One or more heat exchangers areprovided in the low-pressure flow path to warm the gas to apredetermined temperature which is optimum for operation of theelectrochemical pump. Accumulators can be provided in the high-pressureand low-pressure flow paths. The flow paths can be thermally coupled byone or more regenerative heat exchangers. The electrochemical pump canbe adapted to transport either hydronium ions or protons. Protons arepreferably transported using pump components that do not contain water,ammonia or other materials in any chemical form which could enter andcontaminate the gas. Where hydrogen is the cryogen, the high-pressureflow path can be provided with a catalytic surface to convert ortho- topara-hydrogen, and the low-pressure flow path can bear catalysts topromote the para- to ortho-conversion. The system is simple, compact,and has unlimited lifetime potential.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of the invention;

FIG. 2 is a schematic diagram of another embodiment of the invention;

FIG. 3 is a detailed section taken along section lines 3--3 in FIG. 1;

FIG. 4 is a detailed section taken along section lines 4--4 in FIG. 3;and,

FIG. 5 is a graph illustrating how the degree of precooling and heatexchanger effectiveness interact with the pressure rating of theelectrochemical pump to define operating regions of particular systems.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, in an exemplary closed cryogenic cooling system 10an electrochemical pump 12 compresses an ionizable cryogenic gas into ahigh-pressure gas inflow path 14 upstream from a Joule-Thomson flowrestrictor 16. An ionizable cryogenic gas is a gas, such as hydrogen oroxygen, that liquifies at less than about 110° K. at atmosphericpressure and that has an ionic form. Any entrained water vapor must beseparated from the pressurized gas in a desiccator 18 having, forexample, a palladium-silver hydrogen diffusion membrane. Thehigh-pressure gas stream may be routed through an accumulator or otherreservoir 20 before passing through a first auxiliary heat exchanger 22where the gas is cooled to well below its inversion temperature, i.e.,the temperature at which the Joule-Thomson coefficient of thepressurized gas changes sign. This top stage cooling, e.g, to 160° K. orless for hydrogen at 12 MPa pressure, can be accomplished by radiationto free space from a spacecraft. The precooled gas then passes throughthe high-pressure side of a regenerative heat exchanger 24 for furthercooling before adiabatically expanding through the Joule-Thomson flowrestrictor 16, resulting in further cooling. The Joule-Thomson flowrestrictor 16 is a valve or orifice(s) through which the gas stream isallowed to adiabatically expand. For spacecraft applications the flowrestrictor 16 can be a metal foam or porous sinter having a plurality ofparallel-path orifices to avoid single point failure. The throttling canliquify a portion of the gas. The adiabatically expanded gas providescryogenic cooling in a load heat exchanger 26 that is thermally coupledto a cryogenic surface or device such as an electronic component 28. Alow-pressure gas flow path 30 delivers the expanded gas from the loadheat exchanger 24 to the electrochemical pump 12. Flow path 30incorporates the low-pressure side of the regenerative heat exchanger24, so that the cold low-pressure gas cools the pressurized gas prior toentry of the low-pressure gas into a second auxiliary heat exchanger 32,where the low-pressure gas is heated. The warmed low-pressure gas isdelivered on demand to the electrochemical pump 12. To accommodatetransient operating conditions such as pressure surges, a reservoir oraccumulator 34 can also be provided in the low-pressure flow path 30.The closed system 10 can be static sealed, i.e., using welded,gasketless seals, to minimize leakage of the cryogen during prolongedmissions.

Referring to FIG. 2, the warming function of the second auxiliary heatexchanger 32 can be realized by thermally coupling the low-pressure flowpath 30 with the high-pressure flow path 14 upstream of the firstauxiliary heat exchanger 22. Waste heat from other mission componentscan alternatively provide or supplement this warming function. Thelow-pressure gas stream must be warmed to above the freezing point ofwater if water-bearing membranes are employed in the electrochemicalpump 12; otherwise, the gas is warmed to the optimum operatingtemperature of the pump's ionic conductor.

The ortho-para relationships of hydrogen should be considered whenhydrogen is employed as the cryogen. At ambient temperature the orthoform of hydrogen gas prevails under steady state, while para-hydrogenpredominates at liquid hydrogen temperatures. Unless the conversion ofortho to para is catalyzed during cool-down of the gas within thehigh-pressure flow path 14, spontaneous conversion can take place at ornear the Joule-Thomson flow restrictor 16, resulting in a reduction ofcooling capacity. Conversely, during the warming of the gas within thelow-pressure flow path 30 it is advantageous to catalyze the conversionof para to ortho for an efficient process. The catalysts 36, 38 areincorporated onto gas-contacting surfaces of the flow paths 14, 30,preferably in the high-pressure and low-pressure sides of theregenerative heat exchanger 24.

Suitable catalysts 36, 38 for promoting the conversion of ortho-topara-hydrogen include iron oxide catalysts (as described, for example,in Japan Kokai Tokkyo Koho No. JP 7359090, 8/18/73), rhodium phosphinecomplexes (Brown, J. M., et al., J. Organomet. Chem. 255(1): 103--111,1983), certain Group IV-VI transition metal nitrides (Kharlamov, A. I.,et al., Tugoplavkie Nitridy, pp. 62-65, 1983), samarium copper (Boeva,O. A., et al., Kinet. Katal. 24(3): 629-632, 1983),potassium-triphenylene complex (Enoki, T., et al., Mol. Cryst. Liq.Cryst. 96(1-4): 401-411, 1983), titanium and manganese carbides(Kharlamov, A. I., et al., Fiz.-khim. Svoistva Tugoplavk. Soedin, iSplavov, Kiev, pp. 55-58, 1981), chromia-alumina and molybdenum-alumina(Kauffman, D., et al., J. Catal. 71(2): 244-256 , 1981), sodium hydride(Chappell, M. J., et al., J. Res. Inst. Catal., Hokkaido Univ. 28(3):109-117, 1980), certain d-metal borides (Kharlamov, A. I., Kinet. Katal.22(3): 684-689, 1981), chromium potassium sulfate (Sakurai, H., Jpn. J.Appl. Phys. 17(6): 1141-1142, 1978), copper-nickel, and cobalt zeolite.

Referring to FIGS. 3 and 4, the electrochemical pump 12 can be designedwith coaxially disposed elements and have a tubular shape. Alternativelythe elements described below can be arranged in planar, concentric, orhoneycomb stack configurations. A first catalytically active currentcollector 40, having gas-contacting surfaces disposed in the deliveryend 42 of the low-pressure flow path 30, is associated on the downstreamside through an ionic conductor 44 with a second catalytically activecurrent collector 46 having gas-contacting surfaces disposed in thereceiving end 48 of the high-pressure flow path 14. Structural supportelements (not shown) are incorporated into the low-pressure side tosupport the ionic conductor 44 against the high-pressure gas. If theionic conductor 44 is a membrane, the first catalytically active currentcollector 40 should be strong enough to bear the compressive load andshould have pores sufficiently small to support the membrane 44 withoutdamage.

As described in U.S. Pat. Nos. 3,475,302, 3,489,670, and 4,118,299 (allincorporated by reference), the pump 12 transports hydrogen by:

(1) converting hydrogen gas to hydrogen ions, either protons (H+) orhydronium ions (H₃ O⁺), using a catalyst at the first current collector40;

(2) transporting the hydrogen ions through the ionic conductor 44, usingan electrical potential applied between the current collectors 40, 46;and,

(3) reconverting the transported hydrogen ions to hydrogen gas using acatalyst at the second current collector 46.

For electrochemical pumps 12 employing hydronium ion conductors 44 theabove steps include the conversion of hydrogen gas to hydronium ions:

    H.sub.2 +2H.sub.2 O→2e.sup.- +2H.sub.3 O.sup.+

catalyzed by, e.g., platinum at an anode that serves as the firstcurrent collector 40; and conversion of transported hydronium ions tohydrogen gas:

    2H.sub.3 O.sup.+ +2e.sup.- →H.sub.2 +2H.sub.2 O

catalyzed by, e.g., platinum at a cathode 42 at the high-pressure sideof the pump 12. The water byproduct must be removed from thehigh-pressure gas stream or the Joule-Thomson flow restrictor 16 willfreeze shut. Complete separation of water vapor from hydrogen gas can beaccomplished by diffusion through a palladium-silver alloy (75:25 wt%;Platin. Metals Rev. 7: 126, 1963) disposed at or near the receiving end48 of the high-pressure flow path 14. The separated water may be storedor returned to the ionic conductor 44 by active or passive means. Asystem 10 that incorporates a water-bearing ionic conductor 44 alsorequires heating of the low-pressure gas stream to above the freezingpoint of water, necessitating an energy consumption that may adverselyaffect the overall efficiency of the system 10 and other missioncomponents. Water-bearing ionic conductors include solid, hydratedmembranes and other materials in which water molecules are absorbed orchemically combined, as well as wetted materials containing water insolution.

An electrochemical hydronium ion pump may contain a platinum catalyst onboth sides of a NAFION membrane (#117 or 125; Du Pont). Thecatalyst-coated membrane is sandwiched between and in mutual contactwith a pair of porous, sintered plates such as niobium that serve as theanode and cathode. The pores in these current collectors are sized justlarge enough to permit unrestricted passage of hydrogen or oxygen gasmolecules. The membrane can alternatively be sandwiched betweenplatinum-coated sides of porous carbon paper or cloth, with structuralsupport provided by fine-mesh niobium screens, porous ceramic, plastic,or other inert material. Wetted conductors such as asbestos saturatedwith potassium hydroxide solution may be used in conjunction withcatalytically active current collectors, e.g., platinum/teflon/carbonpaper or platinum-coated palladium-silver alloy, that contain the waterwithin the ionic conductor. The vapor barrier should be incorporatedinto at least the downstream side of the pump.

For electrochemical pumps 12 employing hydrogen ion (proton) conductors44 the foregoing conversion steps include dissociation of hydrogen gasto protons and electrons:

    H.sub.2 →2e.sup.- +2H.sup.+

catalyzed by, e.g., platinum at an anode 40; and conversion oftransported protons to hydrogen gas:

    2H.sup.+ +2e.sup.- →H.sub.2

catalyzed by, e.g., platinum at a cathode 42. The provision of hydrogenion (proton) conductors 44 that contain no water, e.g., protonconducting fluoride glasses, hydrogen-beta-alumina, HTaWO₆ and KTaO₃ceramics, eliminates the need for water management in the system 10.Such proton conductors can also be made very thin, on the order of 15microns or less, to compensate for their relatively low conductivity.Suitable proton conductors, some of which contain no water, are listedin TABLE III, R. A. Huggins, Solid Electrolytes, in Materials forAdvanced Batteries, D. W. Murphy, et al., eds., Plenum Press, N.Y., pp.91-110, 1979. Proton-conducting halide glasses that are consideredlikely candidates for the subject water-less systems are disclosed bySchroder, J., Angew. Chem., internat. ed. 3: 376, 1964. Protonconducting complex metal oxides, e.g., HTaWO₆, are disclosed in PhysicsRev., B-19, 54-55, 1979. Other proton conductors are disclosed in: J.Am. Chem. Soc. 65(5): C71, 1982; Z. Phys. Chem. (Wiesbaden) 110(2):285-288, 1978; Amorphous Liq. Semicond., Proc. Int'l. Conf., 5th, Vol.2, pp. 1173-1177, Stuke, J., ed., Taylor and Francis, London, 1973; J.Non-Cryst. Solids 15(2): 191-198, 1974; J. Non-Cryst. Solids 51(3):357-365, 1982; Shilton, M. G., et al., in Fast Ion Transport in Solids:Electrodes and Electrolytes, Vashishta, P., et al., eds., Elsevier NorthHolland, N.Y., pp. 727-730, 1979; Z. Phys. Chem. (Wiesbaden) 110(2):285-288, 1978; J. Applied Physics 42(8): 3121-3124, 1971; J. PolymerScience: Polymer Chemistry Ed. 10(11): 3447-3450, 1972; Annual technicalreport June 1, '73-May 31, '74, and Semiannual techincal report June1,-Nov. 30, 1973, Contract No: DAHC-15-73-G11; ARPA Order-2338; U.S.Pat. No. 4,513,069; Wiseman, P. J., Particle hydrates as protonconductors, in Progress in Solid Electrolytes, Wheat, T. A., et al.,eds., CANMET, Canada, pp. 199-202, 1983; all incorporated by reference.

In an exemplary proton pump a 15-micron layer of conducting fluorideglass or NH₄ TaWO₆ ceramic (Specht, R., D. Brunner & G. Tominol,Proton-conducting ceramic, in Amer. Ceramic Soc. 87th Annual Mtg., Abs.87-E-85, May 1985) is coated on both sides with platinum catalyst andsandwiched between patterned niobium or gold current collectors appliedto porous ceramic supports.

The maximum amount of cooling obtained per pound of hydrogen circulatedthrough the system 10 is senitive to both the degree of precooling andthe heat exchanger efficiency. FIG. 5 presents the results of a typicalthermodynamic calculation showing that up to 55 BTU/lb of H₂ (128.0kJ/kg) is obtainable using precooling to 100° K. The optimum pressurefor minimum hydrogen flow under ideal conditions is approximately 2400psia (16.5 MPa). However, this is not necessarily the engineeringoptimum pressure for minimum weight or minimum energy consumption,especially under non-ideal conditions considering losses andinefficiencies. For example, operating at such a high pressure producesa small temperature rise during the Joule-Thomson expansion prior to themain cooling that is produced during expansion, and that could burdenthe design of the heat exchanger. Thus, lower operating pressures in therange of about 1500 to about 1900 psia (10.3 to 13.1 MPa) may bepreferable for systems 10 with imperfect heat exchangers and diffusionlosses. Overall performance is shown in FIG. 5 to be very sensitive toheat exchanger effectiveness, with preference for heat exchangers havingefficiencies of at least 95%. In a preferred embodiment the heatexchangers in the system have effectiveness on the order of 98-99%.

In a representative system 10 employing a hydronium ion pump with asolid electrolyte membrane, hydrogen gas is pressurized to about 7-14MPa, preferably to 12 MPa, before top stage cooling to about 70°-100°K., preferably to 70° K. The pressurized gas is further cooled to about14°-30° K., preferably to 20° K., in a regenerative heat exchangerhaving an effectiveness on the order of 99% before throttling to about0.01-1.2 MPa. The expanded gas stream is warmed to about 290°-360° K.,preferably to 325° K., before entering an electrochemical pump havingpower requirements of about 100 W_(electric) /W_(cooling). Hydrogen flowrate through the system is on the order of 5 mg/sec/watt_(cooling). Forintermittent use the system shown in FIG. 2 is started without applyinga load in the load heat exchanger and with a small mass flow rate suchthat the top stage cooling in the first auxiliary heat exchanger issufficient to bring the gas below the inversion temperature. The massflow rate is increased as the low-pressure sides of the heat exchangersbecome primed with cold gas.

In a related embodiment a closed cycle cryogenic cooling systemoperating on oxygen provides cooling to 94° K. without the use of movingparts. The oxygen system is similar to the system 10 shown in FIG. 2,except that provision need not be made for the ortho-/para-hydrogenconversion catalysts. Also, the need for precooling by the firstauxiliary heat exchanger is considerably reduced with an oxyen cryogen,since the inversion temperature may be in excess of room temperature.

An electrochemical pump for oxygen can employ an ionic conductor 44 thattransports either oxygen ions or hydronium ions. For example, Bi₂ O₃ isgood oxygen conductor operating at room temperature; (Bi₂ O₃)₀.6(PbO)₀.25 (CaO)₀.15 is a suitable oxygen ion solid electrolyte.Yttria-doped zirconia is suitable for conducting oxygen ions at highertemperatures in conjunction with praseodymium oxide catalysts. Otheroxygen conductors include the cathode materials disclosed at pages 15-17of CANMET Division Report ERP/MQL 83-120 (IR), August 1983, and at pages281-285 of Subbarao, E. C., et al., Oxide electrolytes with fluoridestructure, in Progress in Solid Electrolytes, Wheat, T. A., et al.,eds., CANMET, Canada, pp. 283-285, 1983; both incorporated by reference.

The maximum amount of cooling obtained per pound of oxygen circulatedthrough the system is sensitive to the degree of precooling and the heatexchanger efficiency. For example, with a typical operating pressure of2000 psia (13.8 MPa), the theoretical cooling available withoutprecooling (21° C. operation) is 12 BTU/lb (27.9 kJ/kg) of O₂ ;precooling to -40° C. (233° K.) doubles the amount of cooling available.

While preferred embodiments of the invention have been described, one ofordinary skill after reading the foregoing specification will be able toeffect various changes, substitutions of equivalents, and otheralterations to the system and method set forth herein. The descriptionis intended to illustrate the invention and is not meant to limit it,unless such limitation is necessary to avoid the pertinent prior art.Therefore, the protection granted by Letters Patent should be limitedonly by the definition contained in the appended claims and equivalentsthereof.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A closed system with nomoving parts for providing cryogenic cooling to a load heat exchanger,comprising:(a) an electrochemical pump for pressurizing an ionizablecryogenic gas; (b) a high-pressure flow path adapted to directpressurized gas from the electrochemical pump to the load heatexchanger, the path including a first heat exchanger for cooling the gasto below its inversion temperature and a Joule-Thomson flow restrictorto further cool the gas to a cryogenic temperature for delivery to theload heat exchanger; and, (c) a low-pressure flow path adapted toreceive the gas from the load heat exchanger and to return the gas tothe electrochemical pump, the low-pressure flow path including a secondheat exchanger for warming the gas to a predetermined temperature. 2.The system of claim 1 wherein the load heat exchanger is adapted toprovide cryogenic cooling to an electronic component.
 3. The system ofclaim 1 wherein the ionizable cryogenic gas is selected from the groupconsisting of hydrogen and oxygen.
 4. The system of claim 3 wherein theionizable cryogenic gas is hydrogen.
 5. The system of claim 4 furthercomprising first and second catalyst means, the first catlyst meansincorporated into the high-pressure flow path to convert ortho-hydrogento para-hydrogen, and the second catalyst means incorporated into thelow-pressure flow path to convert para-hydrogen to ortho-hydrogen. 6.The system of claim 5 wherein the first and second catalyst meanscomprise one or more catalysts selected from the group consisting ofiron oxide catalysts, rhodium phosphine complexes, Group IV-VItransition metal nitrides, samarium copper, potassium-triphenylenecomplex, titanium carbide, manganese carbide, chromia-alumina,molybdenum-alumina, sodium hydride, d-metal borides, chromium potassiumsulfate, copper nickel, and cobalt zeolite.
 7. The system of claim 1further comprising a gas reservoir incorporated into the high-pressureflow path.
 8. The system of claim 1 further comprising a reservoirincorporated into the low-pressure flow path.
 9. The system of claim 1further comprising a regenerative heat exchanger thermally coupling thereceiving end of the low-pressure flow path and the delivery end of thehigh-pressure flow path.
 10. The system of claim 1 wherein the secondheat exchanger is thermally coupled to the high-pressure flow pathupstream of the first auxiliary heat exchanger.
 11. The system of claim1 wherein the second heat exchanger warms the gas to above the freezingpoint of water.
 12. The system of claim 1 further comprising desiccatormeans incorporated into the high-pressure flow path.
 13. The system ofclaim 1 wherein the electrochemical pump comprises a hydronium ionconductor.
 14. The system of claim 13 wherein the electrochemical pumpcomprises desiccator means.
 15. The system of claim 1 wherein theelectrochemical pump comprises a proton conductor.
 16. The system ofclaim 15 wherein the electrochemical pump comprises desiccator means.17. The system of claim 15 wherein the proton conductor is a solid,non-hydrated material.
 18. The system of claim 17 wherein the protonconductor is selected from the group consisting of proton-conductinghalide glasses, hydrogen-beta-alumina, NH₄ TaWO₆, HTaWO₆, and KTaO₃. 19.A closed, static-scaled system with no moving parts for providingcooling at about 14°-30° K. to an electronic component, comprising:(a)an electrochemical pump for pressurizing hydrogen gas to about 7-14 MPa;(b) a high-pressure flow path adapted to direct pressurized gas from theelectrochemical pump to a load heat exchanger adapted to provide coolingat about 14°-30° K. to the electronic component, the path including afirst heat exchanger for cooling the gas to about 70°-100° K. and aJoule-Thomson flow restrictor for further cooling the gas to about14°-30° K. for delivery to the load heat exchanger; and, (c) alow-pressure flow path adapted to receive the gas from the load heatexchanger and to return the gas to the electrochemical pump, thelow-pressure flow path including a second heat exchanger for warming thegas to a predetermined temperature.
 20. The system of claim 19 whereinthe gas pressure after passing through the Joule-Thomson flow restrictoris about 0.01-1.2 MPa.
 21. The system of claim 19 wherein the warming inthe second heat exchanger is to about 290°-360° K.
 22. The system ofclaim 21 wherein the electrochemical pump comprises a hydronium ionconductor.
 23. The system of claim 22 wherein the electrochemical pumpcomprises desiccator means.
 24. The system of claim 22 furthercomprising desiccator means in the high-pressure flow path.
 25. Thesystem of claim 19 wherein the hydrogen flow rate is on the order of 5mg/sec/watt cooling.
 26. The system of claim 19 wherein the powerrequirements of the electrochemical pump is on the order of 100W_(electric) /W_(cooling).
 27. The system of claim 19 wherein the firstheat exchanger is adapted to cool the pressurized gas by radiation tospace.
 28. The system of claim 19 wherein the Joule-Thomson flowrestrictor comprises a plurality of orifices.